1. Field of Invention
The invention relates to an automatic engine stop/restart-type vehicle having an engine that is stopped automatically upon fulfillment of a predetermined one of running conditions of the vehicle, to a method of controlling the vehicle, and to an apparatus that stops an engine automatically.
2. Description of Related Art
A vehicle having an engine that is stopped automatically upon fulfillment of a predetermined one of running conditions of the vehicle and that is restarted automatically for takeoff by a certain operation performed by a driver such as depression of an accelerator pedal is known for a long time as a so-called economy running vehicle. In the case where an automatic transmission is adopted in such an automatic engine stop/restart-type vehicle, a mechanical oil pump driven by an engine maintains hydraulic fluid in a friction coupling element and a change-gear mechanism of the automatic transmission at a certain pressure. If the engine is stopped automatically upon fulfillment of a predetermined running condition of the vehicle, the mechanical oil pump driven by the engine is stopped as well. For this reason it becomes impossible to maintain hydraulic fluid in the automatic transmission at a certain pressure when the engine is restarted.
In an attempt to solve this problem, Japanese Patent Application Laid-Open No. 8-14076 discloses holding forward clutches in an automatic transmission in an engaged state even during stoppage of an engine by installing an accumulator. As another solution, Japanese Patent Application Laid-Open No. 10-324177 discloses the idea of additionally providing an electric oil pump capable of supplying a hydraulic pressure at which a forward or backward friction coupling element is about to be coupled if an engine is stopped while a vehicle is running with a shift lever at a forward or backward position.
FIG. 5 is an exemplary diagram showing how component members of a typical economy-running vehicle are arranged in relation to one another, and how an electric oil pump is arranged in relation to the other component members. (The controller 100 of FIG. 5 is part of the present invention, and is not prior art.) An output torque of an engine 1 is input to an automatic transmission 3 via a torque converter 2 and output to an output shaft 4 of a vehicle. An electric oil pump 6 is disposed in parallel with a mechanical oil pump 5 driven by the engine 1. An output from the electric oil pump 6 is combined with an output from the mechanical oil pump 5 via a check valve 7 and then transmitted to the automatic transmission 3. The electric oil pump 6 is supplied with electric power from a battery 8 via a driver circuit 9, which is connected to an oil pump control device 10.
It will now be described how the typical construction (without controller 100 of the invention) operates. When the engine 1 is running, an output torque of the engine 1 is output to the output shaft 4 via the torque converter 2 and the automatic transmission 3, and drives the mechanical oil pump 5 at the same time. A hydraulic pressure generated at this moment is transmitted through a hydraulic circuit and suitably controlled by hydraulic pressure control means (not shown). The hydraulic pressure thus controlled is supplied to the automatic transmission 3. On the other hand, if the engine 1 is stopped automatically and assumes an economy-running state, the mechanical oil pump 5 stops operating and no longer generates a hydraulic pressure. In this case, the oil pump control device 10 transmits a drive signal for controlling operation of the electric oil pump 6 to the driver circuit 9, such that the electric oil pump 6 is operated. Electric power in the battery 8 is then supplied to the electric oil pump 6 via the driver circuit 9, such that the electric oil pump 6 is operated and generates a hydraulic pressure. This hydraulic pressure is transmitted through the hydraulic circuit via the check valve 7, suitably controlled by the hydraulic pressure control means (not shown), and supplied to the automatic transmission 3. The check valve 7 prevents a high hydraulic pressure in the mechanical oil pump 5 from being transmitted back to the electric oil pump 6.
It is not the mechanical oil pump 5, but the electric oil pump 6 that operates when the engine is out of operation. The electric oil pump 6 maintains hydraulic fluid in the change-gear mechanism and the friction coupling element at a certain pressure. As a result, the engine can be restarted appropriately.
For example, according to Japanese Patent Application Laid-Open No. 10-324177 mentioned above, if the engine is stopped while the vehicle is running with the shift lever at the forward or backward position, the electric oil pump capable of supplying a hydraulic pressure at which the forward or backward friction coupling element is about to be coupled is additionally provided, whereby a shock caused during restart of the engine is absorbed. As a result, it becomes possible to improve driveability of the vehicle.
In the case where a manually set mode of the automatic transmission is shifted from a non-running range (N or P range) to a running range (D or R range), the following problem arises. For instance, if an accelerator pedal and a brake pedal have been turned off and on respectively while the vehicle is stopped, setting the manually set mode as a non-running range is defined as an economy-running condition in a strict sense for convenience of explanation. Even if this economy-running condition in a strict sense is fulfilled, the vehicle sometimes remains in a non-economy-running state in which the engine is in operation without shifting to a so-called economy-running state in which the engine is stopped automatically. That is, the vehicle is designed in principle not to stop the engine if it is necessary to refrain from stopping the engine for reasons of the maintenance of basic systems of the vehicle. Fulfillment of a condition required for the maintenance of the systems can be defined as an economy-running condition in a broad sense. Even if the economy-running condition in a strict sense is fulfilled, the engine is not stopped automatically unless the economy-running condition in a broad sense is fulfilled. For instance, the economy-running condition in a broad sense may be that the battery has a sufficient amount SOC of charge, that a booster of the brake making use of a negative pressure in the engine is at a sufficient negative pressure, or that a condition concerning the temperature of coolant is fulfilled.
Accordingly, when the vehicle is in a non-running range, there are two cases, that is, the case of a non-economy-running state in which the engine is running with the economy-running condition in a broad sense unfulfilled and the case of an economy-running state in which the engine has been stopped automatically with both the economy-running condition in a strict sense and the economy-running condition in a broad sense fulfilled. If a so-called garage shift for changing the manually set mode from a non-running range to a running range is taken into account, it becomes apparent that there are two cases, namely, the first case where a garage shift is made while the engine is running and the second case where a garage shift is made while the engine has been stopped automatically.
In the first case where a shift is made from a non-running range to a running range in a non-economy-running state in which the engine is running, since the engine generates a torque and the mechanical oil pump is in operation, the original hydraulic pressure supplied to the automatic transmission is sufficiently high. On the other hand, in the second case where a shift is made from a non-running range to a running range in an economy-running state in which the engine has been stopped automatically, since the engine does not generate a torque and the mechanical oil pump is out of operation, the original hydraulic pressure supplied to the automatic transmission is lower as compared with the first case. This hydraulic pressure is supplied, for example, from the electric oil pump. Because the friction coupling element in the automatic transmission is in a disengaged state when the vehicle is in a non-running range, such as N range or P range, the first and second cases are significantly different from each other in terms of conformity between friction coupling characteristics of the friction coupling element based on the rising of the hydraulic pressure supplied to the automatic transmission and input characteristics of the automatic transmission based on the rising of the torque generated by the engine. Therefore, optimal transition characteristics and optimal speed-change characteristics cannot be achieved if the first and second cases are handled in the same manner. As a result, driveability of the vehicle is a problem.
In the case where the manually set mode of the automatic transmission is thus shifted from a non-running range to a running range, the problem regarding conformity between friction coupling characteristics of the friction coupling element and input characteristics of the automatic transmission is caused as described above. However, there is no related art offering a desirable solution to the problem.
It is an object of the invention to provide a vehicle capable of solving the problem regarding conformity between friction coupling characteristics of a coupling element (such as an axle clutch) and input characteristics of an automatic transmission in the case where a manually set mode of the automatic transmission is shifted from a non-running range to a running range and achieving optimal transition characteristics and optimal speed-change characteristics. It is also an object of the invention to provide a method of controlling the vehicle. It is further an object of the invention to provide an apparatus that stops an engine automatically.
A vehicle according to a first aspect of the invention has an engine, an automatic transmission having a coupling element for transmitting an output torque of the engine, an oil pump for supplying a hydraulic pressure to the automatic transmission, and a controller that: controls an output from the engine, and controls a hydraulic pressure supplied to the automatic transmission. The engine is stopped automatically upon fulfillment of a predetermined one of running conditions of the vehicle. The controller determines whether or not the engine is in an automatic stop state when a manually set mode of the automatic transmission is shifted from a non-running range to a running range. Hydraulic pressure compensation control is performed by the controller so as to conform friction coupling characteristics of the coupling element and input characteristics of the automatic transmission with each other if the controller determines that the engine is in an automatic stop state.
According to the aforementioned first aspect of the invention, the controller determines whether or not the engine is in an automatic stop state when the manually set mode of the automatic transmission is shifted from a non-running range to a running range. The controller performs hydraulic pressure compensation control if the controller determines that the engine is in an automatic stop state. The problem regarding conformity between friction coupling characteristics of the friction coupling element and input characteristics of the automatic transmission is thus prevented from being caused due to a difference in original hydraulic pressures supplied to the automatic transmission in the case where the manually set mode is shifted from a non-running range to a running range. As a result, optimal transition characteristics and optimal speed-change characteristics can be achieved.
A vehicle according to a second aspect of the invention has an engine, an automatic transmission having a friction coupling element for transmitting an output torque of the engine, an oil pump for supplying a hydraulic pressure to the automatic transmission, and a controller that: controls an output from the engine, controls a hydraulic pressure supplied to the automatic transmission. The engine is stopped automatically upon fulfillment of a predetermined one of running conditions of the vehicle. The controller determines whether or not the engine is in an automatic stop state when a manually set mode of the automatic transmission is shifted from a non-running range to a running range. Loosening control of throttle opening characteristics is performed in relation to an accelerator opening so as to conform friction coupling characteristics of friction coupling element and input characteristics of the automatic transmission with each other if the controller determines that the engine is in an automatic stop state.
According to the aforementioned second aspect, the controller determines whether or not the engine is in an automatic stop state when the manually set mode of the automatic transmission is shifted from a non-running range to a running range. The controller performs loosening control of the throttle opening characteristics in relation to the accelerator opening if the controller determines that the engine is in an automatic stop state.
Therefore, the problem regarding conformity between the friction coupling characteristics of the friction coupling element and the input characteristics of the automatic transmission can be prevented from being caused due to a difference in delays of the rising of the friction coupling characteristics of the friction coupling element when the manually set mode is shifted from a non-running range to a running range. As a result, optimal transition characteristics and optimal speed-change characteristics can be achieved.
A vehicle according to a third aspect of the invention has an engine, an automatic transmission having a friction coupling element for transmitting an output torque of the engine, an oil pump for supplying a hydraulic pressure to the automatic transmission, and a controller that: controls an output from the engine, controls a hydraulic pressure supplied to the automatic transmission. The engine is stopped automatically upon fulfillment of a predetermined one of running conditions of the vehicle. The controller determines whether or not the engine is in an automatic stop state when a manually set mode of the automatic transmission is shifted from a non-running range to a running range. Anti-squat shifting control for absorbing an impact caused in changing the manually set mode of the automatic transmission is prohibited so as to conform friction coupling characteristics of friction coupling element and input characteristics of the automatic transmission with each other if the non-running range state determination element determines that the engine is in an automatic stop state.
According to the aforementioned third aspect of the invention, the controller determines whether or not the engine is in an automatic stop state when a manually set mode of the automatic transmission is shifted from a non-running range to a running range. Anti-squat shifting control for absorbing an impact during the shift of the manually set mode is prohibited from being performed in the automatic transmission if the controller determines that the engine is in an automatic stop state. Accordingly, a time lag in the rising of the torque of the output shaft can be prevented from being caused when the manually set mode is shifted from the non-running range to the running range. As a result, it becomes possible to solve the problem regarding conformity between the friction coupling characteristics of the friction coupling element and the input characteristics of the automatic transmission and achieve optimal transition characteristics and optimal speed-change characteristics.